Polyoxovanadate-based MOFs: Multi-site efficient catalytic epoxidation of olefins

Catalytic epoxidation of olefins has garnered significant attention due to the important of epoxides as organic intermediates. Nevertheless, existing methodologies are often encumbered by environmental concerns, elevated costs, and the inability to achieve efficient epoxidation of both terminal and internal olefins concurrently. Consequently, to develop olefin epoxidation using oxygen as an oxidant under mild conditions has become a highly sought-after goal. In this paper, polyoxovanadates, which can activate oxygen, were employed as building units, and three isostructural polyoxovanadate-based metal-organic frameworks (POV-MOFs): M(azpy)V 2 O 6 (M=Co for 1 , Ni for 2 , and Zn for 3 ; azpy = 4, 4′-azobispyridine) were constructed. Single crystal diffraction analysis revealed that they comprised of transition metal M (Co 2 + , Ni 2+ , and Zn 2+ ) and {V 2 O 6 } 2- clusters. Among them, compound 1 , constructed by Co 2+ , exhibits clear advantages over compounds 2 and 3 , constructed by Ni 2+ and Zn 2+ , in catalyzing the selective oxidation of internal olefins and terminal olefins to the corresponding epoxides. At near room temperature , compound 1 can achieve 99 % conversion of internal olefin-type cyclooctene to cyclooctene oxide in 3 h, and 99 % selectivity, with 99 % conversion and 94 % selectivity of terminal olefin-type styrene to styrene oxide in 1.5 h. Further investigations revealed that both the Co²⁺ and the {V₂O₆} cluster in compound 1 all can independently catalyze the epoxidation of olefins. • Focus on green, energy-saving, and efficient synthesis epoxides from olefins, three polyoxovanadate-based MOFs (Co, Ni, Zn) were rationally designed and synthesized to serve as catalysts according to the reaction mechanism. • At present, there are many reports on the catalysts for olefin epoxidation, but only a few catalysts can simultaneously catalyze the epoxidation of internal olefins and terminal olefins. Catalyst 1 reported in this work can simultaneously achieve efficient catalytic epoxidation of internal olefins and terminal olefins. • Catalyst 1 contains two catalytic sites, the{V 2 O 6 } 2- site and Co 2+ site, which can simultaneously carry out olefin epoxidation according to different paths, which greatly improves the activity of the catalyst. • Catalyst 1 demonstrates outstanding catalytic performance and sustainability in the epoxidation of olefins reaction. After five cycles, it still maintains favorable selectivity and conversion rates. • The concept of integrating {V 2 O 6 } 2- , which can activate O 2 , with Co 2+ , which can activate O 2 , provides valuable guidance for future catalyst design and research endeavors.